diff --git a/applications/proof_of_work_app.go b/applications/proof_of_work_app.go
index bdf0c61..87c8743 100644
--- a/applications/proof_of_work_app.go
+++ b/applications/proof_of_work_app.go
@@ -87,6 +87,9 @@ func (powapp *ProofOfWorkApplication) solveChallenge(challenge []byte, prng core
 
 // ValidateChallenge returns true if the message and spamguard pass the challenge
 func (powapp *ProofOfWorkApplication) validateChallenge(challenge []byte, solution []byte) bool {
+	if len(solution) != 32 {
+		return false
+	}
 	solve := make([]byte, len(challenge)+32)
 	copy(solve[0:], solution[0:32])
 	copy(solve[32:], challenge[:])